Effect of Amines as Corrosion Inhibitors for a Low Carbon Steel in Power Industry

80 Pages·2005·2.34 MB·English

by  Díaz, Jorge G.

EFFECT OF AMINES AS CORROSION INHIBITORS FOR

A LOW CARBON STEEL IN POWER INDUSTRY

Jorge G . Díaz

Thesis Prepared for the Degree of

MASTER OF SCIENCE

UNIVERSITY O F NORTH TEXAS

Decem ber 2004

APPROVED:

Seifollah Nasrazadani, Major Professor

Philip Foster, Committee Member

Reza Mirshams, Committee Member

Robert Thiemer, Committee Member

Albert Grubbs, Chair of Engineering Technology

Department
Oscar Garcia, Dean of College of Engineering
Sandra L. Terrell, Dean of the Robert B. Toulouse
School of Graduate Studies
Díaz, Jorge G., Effect of Amines as Corrosion Inhibitors for a Low Carbon Steel in
Power Industry, Master of Science (Engineering Technology), December 2004, 72 pp., 5 tables,
31 figures, references 48 titles.
Commonly used amines in power industry, including morpholine, DBU (1,8-
diazabicyclo[5.4.0]undec-7-ene), and DMA (dimethylallylamine) were evaluated for their effect
on AISI 1018 steel at 250oF. Samples were exposed to an autoclave containing amine added
aqueous solution at pH of 9.5 for 1, 2, 4, 6, 8, and 12 hours. Morphology studies were carried
using scanning electron microscope (SEM), phase analysis was done utilizing Fourier transform
infrared spectroscopy (FTIR), and weight loss was performed to assess kinetics of oxidation.
Control samples showed the highest metal dissolution rate. DBU showed the best performance in
metal protection and SEM indicated the presence of a free-crack layer formed by fine particles in
that set. FTIR showed that DBU apparently favored the formation of magnetite. It is believed
that fine particles impede intrusion of aggressive ions into the metal surface by forming a barrier
layer. FTIR demonstrated that DMA formed more oxyhydroxides, whereas morpholine presented
magnetite to hematite transformation as early as 2 hours. SEM revealed that control and DMA
produced acicular particles characteristic of oxyhydroxides while morpholine and DBU
presented more equiaxed particles.
ACKNOWLEDGEMENTS

I would like to express my deep regards to my committee chair Dr. Seifollah Nasrazadani
for his extraordinary guidance and support in every way possible in completion of this research
work. I would also like to thank my other committee members, Dr. Phillip Foster, Dr. Reza
Mirshams, and Mr. Robert Theimer (TXU, Glenn Rose) for their helpful observations to improve
this work. I would also like to thank Mr. Jim Stevens (TXU, Glenn Rose), Dr. Teresa Golden
(Chemistry Department, University of North Texas), Dr. Rick Reidy, and Rosa Orozco (both
Materials Science Department, University of North Texas), and my colleague Ms. Haritha
Namduri for her consistent encouragement and help without which this research would not have
been completed on time.
On a more personal level I want to thank my family for their encouragement, moral and
financial support, and Dr. S. Nasrazadani for his invaluable help, and guidance. God bless them.

ii
TABLE OF CONTENTS

Page

ACKNOWLEDGEMENTS..........................................................................................................ii

LIST OF TABLES........................................................................................................................v

LIST OF FIGURES.....................................................................................................................vi

Chapters

I. INTRODUCTION................................................................................................1
Corrosion Basics.......................................................................................3
Corrosion Mechanism...............................................................................3
Corrosion in Secondary Side Components...............................................6
Iron Corrosion Mechanism and Oxides....................................................8

II. LITERATURE REVIEW...................................................................................13
Classification and Selection of Inhibitors in Power Industry.................16
Amines....................................................................................................18
Particle Size............................................................................................20
Effect of Amines in Deposit Formation..................................................20

III. EXPERIMENTAL PROCEDURE.....................................................................23
Preparation of Specimens.......................................................................23
Physical Analysis....................................................................................24
Chemical Analysis..................................................................................24
Scanning Electron Microscope (SEM)...................................................24
Fourier Transform Infrared Spectroscopy (FTIR)..................................25
Weight Loss Analysis.............................................................................28
Samples Identification System................................................................29

IV. RESULTS AND DISCUSSION.........................................................................30
Kinetics Studies..................................................................................................30
Morphological Analysis Using Scanning Electron Microscopy.............31
Morphological Analysis of Steel Samples Exposed to Plain Steam
.....................................................................................................32
iii
Morphological Analysis of Steel Samples Exposed to Steam with
DBU............................................................................................35
Morphological Analysis of Steel Samples Exposed to Steam +
Morpholine..................................................................................39
Morphological Analysis of Steel Samples Exposed to Plain Steam
with DMA...................................................................................43
Summary of Morphological Features.........................................47
Phase Formation and Transformation Analysis Using FTIR..................47
FTIR Analysis of Steel Samples Exposed to Plain Steam..........48
FTIR Analysis of Steel Samples Exposed to Steam with DBU
.....................................................................................................49
FTIR Analysis of Steel Samples Exposed to Steam with
Morpholine..................................................................................49
FTIR Analysis of Steel Samples Exposed to Steam with DMA
.....................................................................................................49

V. CONCLUSIONS.................................................................................................62
Recommendations for Future Work........................................................64

APPENDIX.................................................................................................................................65

REFERENCES...........................................................................................................................69

iv
LIST OF TABLES

Page

1. Iron oxides and oxyhydroxides.........................................................................................9
2. Chemical composition of steel used for experiments.....................................................24
3. FTIR absorption bands for some iron oxides and oxyhydroxides..................................27
4. Summary of iron oxides and oxyhydroxides phases identified by FTIR........................51
5. Summary of morphologies identified by SEM...............................................................52

v
LIST OF FIGURES

Page

1. Rankine cycle and stages of the working fluid.................................................................2
2. Schematic of metal dissolution in acidic media................................................................4
3. Common problems and their most common localization on the secondary side..............9
4. Pathway of transformation mechanisms accepted for some iron oxides........................11
5. Representation of iron oxides and their transformation with associated mechanisms...12
6. Influence of steam quality over pH for different amines................................................22
7. Schematic of SEM..........................................................................................................26
8. Schematic diagram of an IR absorption instrument........................................................28
9. Schematic diagram of an IR Reflectance module...........................................................29
10. Weight loss plot for AISI 1018 steel samples exposed to plain and amine containing
steam for different exposure times at 250 °F..................................................................31
11. SEM micrographs of steel coupons exposed to clean steam for 1 hour.........................32
12. SEM micrographs of steel coupons exposed to clean steam for 2 hours (a, b), 4 hours (c,
d), 6 hours (e, f)...............................................................................................................33
13. SEM micrographs of steel coupons exposed to clean steam for 8 hours (a, b, c and d), and
12 hours (e, f)..................................................................................................................34
14. SEM micrographs of steel coupons exposed to 3ppm DBU + steam for 1 hour (a, b, c),
and 2 hours (d, e, f).........................................................................................................36
15. SEM micrographs of steel coupons exposed to 3ppm DBU + steam for 4 hours (a, b), and
6 hours (c, d, e, and f).....................................................................................................37
16. SEM micrographs of steel coupons exposed to 3ppm DBU + steam for 8 hours (a, b, and
c), and 12 hours (d, e, and f)...........................................................................................38
17. SEM micrographs of steel coupons exposed to 5ppm morpholine + steam for 1 hour (a, b,
and c), and 2 hours (d, e, and f)......................................................................................40
18. SEM micrographs of steel coupons exposed to 5ppm morpholine + steam for 4 hours (a,
b, and c), and 6 hours (d, e, and f)..................................................................................41
vi
19. SEM micrographs of steel coupons exposed to 5ppm morpholine + steam for 8 hours (a,
b, c, and d), and 12 hours (e and f).................................................................................42
20. SEM micrographs of steel coupons exposed to 3ppm DMA + steam for 1 hour (a, b, and
c), and 2 hours (d, e and f)..............................................................................................44
21. SEM micrographs of steel coupons exposed to 3ppm DMA + steam for 4 hours (a, and
b), and 6 hours (c, d, e, and f).........................................................................................45
22. SEM micrographs of steel coupons exposed to 3ppm DMA + steam for 8 hours (a, b, and
c), and 12 hours (d, e, and f)...........................................................................................46
23. FTIR spectra of oxides formed on steel coupons exposed to steam for 2, 3 and 4 hours set
at 250 °F..........................................................................................................................53
24. FTIR spectra of oxides formed on steel coupons exposed to steam for 6, 8 and 12 hours
set at 250 °F....................................................................................................................54
25. FTIR spectra of oxides formed on steel coupons exposed to steam + 3ppm DBU for 2, 4
and 6 hours set at 250 °F.................................................................................................55
26. FTIR spectra of oxides formed on steel coupons exposed to steam + 3ppm DBU for 8,
and 12 hours set at 250 °F...............................................................................................56
27. FTIR spectra of oxides formed on steel coupons exposed to steam + 5ppm morpholine
for 1, 2 and 4 hours set at 250 °F....................................................................................57
28. FTIR spectra of oxides formed on steel coupons exposed to steam + 5ppm morpholine
for 6, 8 and 12 hours set at 250 °F..................................................................................58
29. FTIR spectra of oxides formed on steel coupons exposed to steam + 3ppm DMA for 1, 2
and 4 hours set at 250 °F.................................................................................................59
30. FTIR spectra of oxides formed on steel coupons exposed to steam + 3ppm DMA for 6, 8
and 12 hours set at 250 °F...............................................................................................60
31. Comparison of FTIR spectra of oxides formed on steel coupons exposed to steam
containing amines for 4 hours set at 250 °F....................................................................61
vii
CHAPTER I
INTRODUCTION

Although corrosion is the thermodynamic method of returning a metal to its lowest
energy form, it is a non-desired situation that destroys cars, pipes, buildings, bridges, plant, and
factories. Every year the cost of maintaining, repairing and inspecting steam generators at U.S.
pressurized water reactors exceeds $100 million. This is approximately equivalent to $1.5
million per plant. These costs are excluding the cost incurred in routine inspection and repair.
French power plants spend similar amounts (Varrin et al., 1996). Steam generator (SG) fouling
involves deposition of iron corrosion mainly magnetite on the tube bundle. The cost of deposit
removal is $3,200/kg when is done chemically. One SG costs from $10 to $25 US million
dollars. Over the last 20 years 27 US plants have replaced 85 SGs and 13 more plants are
planning to replace 34 SGs over the next five years (Klimas et al., 2003).
The secondary cycle is a loop that consists generally of a steam generator, turbines (high
and low pressure) connected to an electric generator, a heat exchanger that condensates the
working fluid (steam), a pump that recirculates the condensate through the steam generator,
feedwater heaters and sometimes condensate demineralizers, among others. The materials for
those components are mild steel for the low pressure/temperature stage, stainless steel, copper
alloys for the feedwater tubing, and nickel alloys (Inconel-600 and Incoloy-800) for the
pressurized water reactor (PWR) which is high pressure/temperature operated (Passell et al.,
1988). Figure 1 shows the schematics of a typical Rankine cycle.

1
Figure 1. Rankine cycle and stages of the working fluid.
The major part of the cost involved in steam generator maintenance is related directly or
indirectly to the formation and transport of corrosion products in the secondary systems. The
accumulated corrosion products in one component increase the chances of other components to
corrode in the secondary cycle. Typical corrosion problems include, stress corrosion cracking
and inter-granular cracking. Corrosion products accumulate forming layers on the tube surfaces,
steam traps, condensers, and other places where condensate might form (Millet and Wood,
1997).
Deposit formation affects the performance of a power plant by lowering the heat transfer
rate, and increasing operational maintenance cost of the power plant. Fouling defined as the
deposition of insoluble oxides and debris onto the surface causes clogging of heat exchanger
tubes. Adequate prevention of fouling is facilitated by physical and chemical characterization of
these deposits. When track of the characteristics are kept, a trend could show when the failure
might happen.
Impurities of the corrosion products are transported due to ongoing erosion and corrosion
by make-up water, condensate and drain systems. Transported matters adhere on the surfaces as
2